This invention relates to a process for producing a magnetic recording medium comprising a support coated with ferromagnetic particles dispersed in a binder. More particularly, the invention relates to a process for producing a magnetic recording medium having a uniform dispersion of magnetic particles and an improved signal-to-noise (S/N) ratio.
Recent expansions in the applications of magnetic recording media have given rise to a demand for a magnetic recording medium having an improved S/N ratio, and this improved S/N ratio is particularly desirable when the medium is video tape or audio tape. Desirable S/N ratios require, among other things, a uniform dispersion of magnetic particles, and the conventional techniques for improving the dispersibility of magnetic particles and reducing tape noise include the following: (1) reducing the size of the magnetic particles; (2) adding a dispersant (e.g., surfactant); (3) adding an agent to prevent particle reaggregation (e.g., solid particles); and (4) using a powerful dispersing mill. However, it has been found that even if a coating solution having a good dispersion of magnetic particles is initially applied to a support, the particles reaggregate during drying to provide a coating in which the particles are no longer dispersed uniformly. A highly viscous coating solution and an agent to prevent the reaggregation of magnetic particles (solid particles) are effective to some extent, but they find only limited utility because the high-viscosity coating solution is difficult to filter and to apply to the support and too large solid particles (e.g., greater than 5 .mu.m in average diameter) cannot be used.